Our present invention relates to coils having a high current-carrying capacity and, more particularly, to coils for use in power equipment such as inductors, transformers and the like.
It is known to provide coils having a high current-carrying capacity by bending, winding, forming, or similarly shaping a metal alloy, having a high electrical conductivity, e.g. copper or a copper alloy, to produce a helix having a desired internal cross section. As the current-carrying capacity of such a coil, e.g. for use in power equipment such as inductors or transformers, increases, the cross section of each turn must also be increased to the point that bending of the bar becomes increasingly difficult and to the point that problems can arise at each bend. It is desirable, therefore, to provide a system for producing coils of high-current-carrying capacity which will not be limited by the need to bend, wind or form heavy bar stock.
It is, therefore, the principal object of the present invention to provide an improved coil, whereby the mentioned drawbacks are obviated.
Another object of the invention is to provide a coil made by a coil-making method which will yield coils of various current-carrying capacities without limitations resulting from the need to bend bar stock in a particular pattern.
It is still another object of the invention to provide an improved coil with improved electrical and mechanical properties and enhanced thermal performance.
Still another object of the invention is to provide a coil which can be made by a coil-making method which is inexpensive to carry out is reproducible and readily repeatable, requires a minimum of skilled labor and machinery and has high versatility as to the configuration and size of the coil to be produced.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention by stamping preferably angular unit elements from sheet or plate material of high electrical conductivity (usually copper, aluminum or an alloy thereof), while providing, at the ends of the legs of the preferably angular element, respective formations enabling interengagement of such elements to define a helix, interfitting the formations of successive elements to form turns of a helix, and fusing the elements together at these formations.
During the stamping step, the formations, which can include a female formation at one end of each element and a complementary male formation at the other end, can be formed simultaneously with the shaping of the elements. In some cases, however, it may be desirable to first stamp out the element and then provide the male and female formation by an additional stamping or shaping process.
It has been found to be most advantageous to provide the formations as generally T shaped elements with a wide head and a narrow shank. Other formation shapes may, of course, also be used provided they enable interengagement of mating ends of successive angular elements and snug interfitting thereof so that an interconnection practically free from contact resistance is provided between the successive elements, especially when the elements have been subjected to fusion. In a highly advantageous embodiment, the head of the formation has a square shape and the shank an elongated or rectangular shape.
While the angularly adjoining legs will have angles between them which depend upon the polygonal shape of the cross section of the coil, i.e. will be 90xc2x0 in the case of a rectangular cross section coil or 120xc2x0 in the case of a hexagonal cross section coil, it is preferred to stamp out the elements so that they have at least two angularly adjoining legs and so that the female formations open laterally on one leg and the male formations project longitudinally from the other leg of, for example, an angular element formed with two legs. The legs of each element can be of equal or different lengths and in a preferred embodiment of the invention, each element is generally L-shaped, but could be U or any other shape.
The fusion according to the invention is preferably a brazing or soldering or welding utilizing a flowable metallic material as a bonding agent. The flowable material may be a brazing composition or a solder and the joints between successive angular elements can be brazed or soldered successively or all at once for the entire coil or in any desired grouping.
More particularly, the method of making the heavy duty electrical coil of the invention can comprise the steps of:
(a) forming a multiplicity of identical elongated electrically conductive elements from at least one plate of electrically conductive material and with each of the elements having a male formation projecting beyond an edge of the respective element at one end and a female formation in the form of a cutout complementary to the male formation and opening at an. edge of an opposite end of the respective element;
(b) fitting the male formations of the elements into the female formations of adjoining elements to form respective joints between adjoining elements at which broad surfaces of the adjoining elements are substantially flush with one another, thereby forming a succession of the elements into successive turns of a helix; and
(c) fusion bonding each male formation of a respective joint to the adjoining element receiving same, thereby producing the coil.
The elements can be formed, as noted, by stamping them or punching them from plates of the electrically conductive material. Assembly can make use of solder paste, metglass or any other appropriate material in a reflow option and, for example, the entire assembly can be fusion bonded with one dip in a solder pot. The windings can be preassembled on a mandrel for soldering and powder coating and it is found that with powder coating, turn-to-turn capacitance can be reduced because of the small a turn-to-turn spacing allowed by the powder coating. The powder coating not only insulates the turns from one another but insulates the turns also from any core which can be provided within the coil.
In structural terms the electrical coil of the invention can thus comprise:
a multiplicity of identical elongated electrically conductive elements stamped from at least one plate of electrically conductive material and with each of the elements having a male formation projecting beyond an edge of the respective element at one end and a female formation in the form of a cutout complementary to the male formation and opening at an edge of an opposite end of the respective element, the male formations of the elements fitting into the female formations of adjoining elements to form respective joints between adjoining elements at which broad surfaces of the adjoining elements are substantially flush with one another, thereby forming successive turns of a helix; and
means for fusion bonding each male formation of a respective joint to the adjoining element receiving same, thereby producing the coil.